1. Field of the Invention
This invention relates to a two-stage naphtha hydrorefining process.
2. Description of the Prior Art
Hydrorefining is a well known process for upgrading a variety of hydrocarbon fractions. Naphtha fractions are subjected to hydrorefining by treating with hydrogen and a hydrorefining catalyst to remove sulfur and nitrogenous compounds which may adversely affect the catalyst used in subsequent treating processes, such as for example, reforming processes. Deep levels of desulfurization, such as those required to produce reforming feeds for multimetallic catalysts are difficult to accomplish in conventional hydrotreating processes.
It is known to presulfide hydrorefining catalysts prior to the hydrorefining step.
A process is known for hydrotreating heavy mineral oils in two stages. The gaseous effluent from the first stage is scrubbed to remove ammonia, light hydrocarbons and hydrogen sulfide. Fresh hydrogen is introduced into the system only at the inlet to the second hydrotreating stage. See U.S. Pat. No. 3,717,571.
A process is known for hydrodesulfurizing a heavy oil. The chargestock is reacted with impure hydrogen gas in a first stage, hydrogen sulfide is removed from the vapor phase first stage effluent, make-up hydrogen is added prior to the second hydrodesulfurization stage. The treat gas from the second stage is recycled to the first stage without removal of hydrogen sulfide. See U.S. Pat. No. 3,847,799.
A multistage hydrodesulfurization process for heavy oils is known in which high purity make-up hydrogen is introduced into the final reaction zone only. See U.S. Pat. No. 3,809,644.
A process is known for hydrotreating residual crude oil in two stages. Fresh hydrogen is fed to the second stage. Hydrogen is recovered from the effluent of the second stage and recycled to the first stage. See U.S. Pat. No. 3,900,390.
A two-stage hydrorefining process for desulfurization of naphtha is known in which hydrogen sulfide and light hydrocarbon gases are removed between stages. The second stage catalyst initially is a non-sulfided catalyst. See U.S. Pat. No. 3,884,797.
It has now been found that a high level of desulfurization of naptha can be obtained in a two-stage hydrorefining process wherein the flow of hydrogen treat gas is integrated in a specific manner.